Module: Recent Climate Change

Summary

This is a data-driven module designed to address key questions about the stability of the Earth’s climate in the past and the factors that drive climate change. This information is essential for students who want to study current climate change using NASA data, and interprets this in a correct historical context

Goals

·Students will investigate how land surface and ocean surface temperatures have changed since 1840.

·This exercise asks students to consider two contrasting interpretations of climate change over the last 2,000 years.

·Both interpretations use a range of proxy data, but the Loehle data specifically excludes tree ring data. Investigate how the level of CO2 level in the atmosphere has changed over the last 50 years.

·Introduce students to the sun spot cycle and consider the relationship between sunspots and total solar irradiance.

·In this exercise students will investigate proxy (carbon 14 from tree rings) evidence for how solar irradiance has changed over the last 2,000 years and then the last 12,000 years.

·This exercise will introduce students to the role of orbital cycles in determining the amount of solar radiation that reaches the Earth’s surface and investigate changes over the last 1,000 years.

·Introduce students to the important role of natural cycles in the oceans and atmosphere in determining global climate.

·To compare the estimated net climate forcing with measured changes in global temperature and consider the impact of volcanism on global temperature.

Context for use

This set of exercises focuses on more recent climate data and addresses questions such as:

·How has the land and ocean temperature record changed over the last 100 years?

·How has the land surface changed over the last 2000 years?

·How much carbon dioxide is in the atmosphere and how is this changing?

·Is the sun responsible for climate change?

·Is the sun responsible for recent climate change?

·What role do natural cycles play in recent climate change?

·What is the overall result of all factors that influence climate?

This module is based on real data, freely available online, but often difficult for inexperienced students to import and analyze. These data have been collected and presented in a format that allows students to make their own analyses and interpretations. Each exercise has two sections: The first a spreadsheet tab with original data; the second, a tab with graphs that students use to answer a set of related questions.

These original data are presented in the hope that students can be encouraged to make their own observations, formulate their own questions, construct their own plots, and reach their own conclusions about the nature of climate change. Faculty may decide to present students with the data first and use the graphs for later interpretation in class.

Links to the spreadsheet and PDF versions of the text are provided at the end of this module.

Activity description and teaching materials

Exercise One:

Global temperature since 1840

Aim: Students will investigate how land surface and ocean surface temperatures have changed since 1840.

Learning Outcome: Students will learn how to measure temperature anomalies, and use the data to identify periods of time when there were significant shifts in the rate of climate change. They will also observe how temperature trends from land and oceans match closely,

Added value: Students can use these data to discuss the differences between the CRU and GISS data sets.

Recent changes in global temperature

Open the spreadsheet attached to this module and click on the first tab. This is global temperature anomaly data from NASA, NCDC and CRU.

·Column A is the year

·Column B is global temperature as determined by the CRU

·Column C is global temperature as determined by GISS

·Column D is ocean temperature as determined UK CRU

·Column E is ocean temperature as determined by the NCDC

1.Look at the global curves and describe how global temperature has changed over the last 100 years.

2.Compare the GISS and CRU data. GISS and CRU use different methods to estimate global temperature, what are these and what difference can it make?

3.Compare the ocean and land datasets. Discuss any differences you see.

4.How fast was the climate warming from 1910 to 1945 and from 1965 to 2010?

5.Why is the warming from 1965 to 2010 probably not due to changes in solar activity?

6.Compare the 1998 values for temperature anomalies on land and in the oceans.

7.Why are these different?

8.What happened this year that made the world warm so suddenly?

Exercise Two:

The climate record of the last 2,000 years

Aim: This exercise asks students to consider two contrasting interpretations of climate change over the last 2,000 years. Both interpretations use a range of proxy data, but the Loehle data specifically excludes tree ring data.

Learning Outcome: Students will identify both the Medieval Warm Period (Anomaly) and Little Ice Age in both data sets, but recognize that the Medieval Warm Period is much more pronounced in the (more limited) data set from Loehle. Students will discuss the reason why these anomalies have become so important in the climate debate and the limitations of data sets that are more representative of the northern hemisphere.

Added Value: Students can consider the advantages, disadvantages and controversies related to tree ring data.

Temperature change over the last 2,000 years

These data are from two sources. Loehle excludes important tree ring data that has provided so much important information about past climate in other analyses and only includes other proxy sources such as corals, ice cores, lake sediments and stalactites. The second data set from Jones and Mann includes tree ring data. Both data sets have a strong northern hemisphere bias.

1.What does this graph represent?

2.What is the age range?

3.Why would anyone want to exclude data?

4.Can you observe the Medieval Warm Period (anomaly) in the data?

5.Can you observe the Little Ice Age in the data?

6.According to each analysis, was there any time over the previous 2,000 years when global temperatures were warmer than today?

7.According to each analysis, was there anytime over the previous 2,000 years when the temperature was rising so fast as over the last 50 years?

8.What is the temperature anomaly they measure?

9.Do both papers use the same base period for analysis?

Exercise Three:

CO2 in the atmosphere

Aim: Investigate how the level of CO2 level in the atmosphere has changed over the last 50 years

Learning Outcome: Students will observe that the rate at which CO2 has been added to the atmosphere has been increasing, and will discuss the impact of seasonal changes on the detail of these data.

Added value: Students could discuss how well greenhouse gases are mixed vertically and horizontally in the atmosphere, and compare this distribution with the distribution of water.

Changes in atmospheric carbon dioxide

These data are from the CO2 observatory on Mauna Loa in Hawaii.

1.What does this graph represent?

2.What is the age range?

3.Why does the graph show so annual cyclicity?

4.Calculate the rate at which CO2 is increasing.

5.Has this been constant over the previous 50 years?

6.Given a constant rate of CO2 production, what will the concentration in the atmosphere be by the years 2100 and 2150?

Exercise Four:

The role of the sun (part one)

Aim: Introduce students to the sun spot cycle and consider the relationship between sunspots and total solar irradiance.

Learning Outcome: Students will identify the 11-year sunspot cycle and natural variation in the intensity of sunspot numbers. They will identify the Dalton Minimum and relate sunspot minima to global temperature during the 20th Century.

Added value: Students can use the data to analyze how closely sunspots follow a consistent 11-year cycle.

Changes in the sun

This table lists sunspot data back to the year 1750 when systematic observations began.

1.What does this graph represent?

2.How many complete cycles have there been since records began.

3.What is the average time between sunspot maxima?

4.What year has the record for the largest number of sunspots?

5.What year has the record for the lowest number of sunspots?

6.Can you spot the Dalton minimum, a time when very cold winter and summer temperatures were recorded in the northern hemisphere?

7.What happened to sunspot intensity between 1940 and 1960?

8.What was happening to global temperature during this time?

9.What has happened to sunspot activity from 2000 to 2010?

10.What impact should this have on global temperature?

Exercise Five:

The role of the sun (part two)

Aim: In this exercise students will investigate proxy (carbon 14 from tree rings) evidence for how solar irradiance has changed over the last 2,000 years and then the last 12,000 years.

Learning Outcome: Students will discover that solar irradiance varies considerably over time. They will identify multiple minima over the last 2,000 years and how solar irradiance has increased considerably since the end of the Maunder Minimum. Students will also observe how solar irradiance is thought to have changed over the last 12,000 years; back as far as the beginning of the most recent interglacial period. Students will observe that the sun’s elevated irradiance today is unusually high compared to the last 8,000 years

Added Value: Students can discuss how reliable proxy data are in the more distant past.

Changes in solar irradiance

These data are based on solar proxies (Carbon 14 from wood dated by dendrochronology) that estimate the level of total solar irradiance before the time that sunspots were observed directly.

1.Look at the first (upper) graph

a.What does the first graph represent?

b.What is the age range?

c.Is this data reliable over the full age range?

2.Over what period was sunspot activity the most intense?

a.Use data from module one to compare activity over this period with both global temperature and solar intensity due to Milankovitch cycles.

b.Discuss any relationships you discover, and determine what impact these should have had on global climate

c.What was the overall trend in solar intensity between 8,000 years ago and 3,000 years ago?

d.When was the last time the sun was as active as it is today?

e.What was the climate like at that time (use Module One).

3.How many prolonged minima with sunspot number lower than 10 can you recognize?

a.How long do these minima last?

b.What impact do they have on global climate?

c.Can you relate any of these periods to important moment in human history?

4.Look at the second (lower) graph

a.What does the graph represent?

b.What is the age range?

c.Is this data reliable over the full age range?

5.What is the general trend in sunspot number from 2,000 to 250 years ago?

a.To help with this exercise, take 20 sunspots as a base line and color everything above 20 and then below 20 with different colors

b.What happens to the frequency of solar minima?

c.Identify the Dalton, Maunder, Spörer, Wolf and Oort solar minima

6.Compare the number of sunspots estimated during the Medieval Warm Period with the number today.

a.If the sun were the only factor responsible for climate change what would we expect to see today?

b.If you take Milankovitch cycles into account, does this make any difference? (Also see following exercise).

Exercise Six:

The role of orbital cycles

Aim: This exercise will introduce students to the role of orbital cycles in determining the amount of solar radiation that reaches the Earth’s surface and investigate changes over the last 1,000 years.

Learning Outcome: Students will observe how orbital cycles have controlled the amount of irradiance from the sun reaching the northern hemisphere over the last 140,000 years. Students will compare the reduction in radiation over the last 1,000 years and observe that there has been a steady decrease in radiation at 65°N of the equator.

Added value: Students can be asked to compare the change in irradiance from orbital cycles (~10 Wm-2) with changes from the 11 year solar cycle (1Wm-2 - 2 Wm-2) and discuss what impact this should have on the climate today in the absence of any other factor.

Changes in the Earth’s Orbit (Milankovitch Cycles)

These data are calculated from knowledge of the regular changes in the Earth’s obliquity (tilt), precession (wobble) and orbit (eccentricity) that impact the amount of solar irradiance reaching the top of the atmosphere at a latitude of 65°N of the equator.

1.What impact would Milankovitch cycles have had on the climate in the Northern Hemisphere during the Medieval Warm Period around 1,000 years ago?

2.What has been happening to the amount of solar insolation arriving at the top of the atmosphere since that time?

3.How would this affect global temperature?

Exercise Seven:

The role of the atmospheric and oceanic cycles

Aim: Introduce students to the important role of natural cycles in the oceans and atmosphere in determining global climate

Learning Outcome: Students will explore how natural variation in the PDO, NAO, ENSO and AMO can influence global climate. They will compare changes in global ocean temperature with the PDO and find some evidence of correlation. They will investigate the ENSO data, recognize ENSO events and determine their periodicity. They will compare data on the AMO with hurricane frequency and suggest reasons for their correlation. Finally they will contrast the poor periodicity of the NAO with the other cycles.

Added value: Students can consider how major excursions in the NAO, as happened during the winter of 2009-2010, are indicative of a systematic change in climate.

Changes in the atmosphere and oceans

These are data on the NAO, PDO, ENSO and AMO, a graph of global ocean temperature is included for reference along with diagrams to compare the PDO and ENSO and the frequency of Atlantic Hurricanes.

1.What does each graph represent?

2.What is the age range of each graph?

3.Now look at the PDO data from 1900 to 2010.

a.Describe what you observe.

b.How much variation is there?

c.Try using excel to fit a polynomial to these data

d.How long are the cycles you can observe?

e.When did the changes you observe occur?

f.How does the pattern of the PDO compare to changes in global temperature?

g.Discuss the significance of the PDO data between 1940-1950

4.Look at the ENSO data.

a.Describe what you observe.

b.Compare this with the PDO data.

5.Look at the period from 1980 to 2010 and describe the relationship over this period between the PDO and ENSO.

6.Locate the 1998 ENSO event.

a.How long did this last?

b.Now look at the temperature data.

c.How long did this ENSO event effect global and ocean temperature?

7.Look at the NAO data.

a.Describe what you observe?

b.Can you see any clear cyclicity or trend in this data?

8.Look at the AMO data

a.What is the wavelength of the cycle you observe?

b.Use the graph of Atlantic Hurricane frequency and determine

c.Which years had more than 4 major hurricanes?

d.Which years had fewer than 4 major hurricanes?

e.Is there any relationship between this observation and the frequency of intense hurricanes?

Exercise Eight:

Net Climate Forcing

Aim: To compare the estimated net climate forcing with measured changes in global temperature and consider the impact of volcanism on global temperature.

Learning Outcome: Students will observe the rapid increase in the rate of climate forcing due to human activity starting in the early 1960’s and compare this with the much lower rate of natural forcing from 1900 to 1960. They will also consider the significant short-term drops in the rate of climate forcing and relate these to the impact of volcanic activity.

Added value: Students can measure and compare the length of time that major volcanic eruptions disrupt the background trend of climate forcing. They can relate the size of each eruption its impact on climate and discuss the likely impact of simultaneous multiple eruptions on global climate.

Net Radiative Forcing

This data is used to estimate the impact of all factors (the total net forcing) on climate.

9.What happened in 1883, 1980 and 1991 that caused major negative spikes in forcing of more than -1 Wm-2?

10.What is the most likely cause of positive forcing between 1920 and 1960?

11.How does the rate of forcing change after 1960?

12.What is the probable reason for this change?

13.If solar intensity increases, and more greenhouse gases are added to the atmosphere how will the net radiative forcing relative to 1880 change over the next 50 years?

Teaching notes

Instructions:

Open the spreadsheet (see below) and click on the tab for the first exercise. Each exercise has two tabs: one for the data and a second with some graphical analysis to help you with your answer these questions.